An event-based hierarchical control framework is presented for the control of power flow in vehicle systems. With multiple systems and subsystems interacting over a wide range of timescales, the control performance of vehicle systems can be significantly improved using hierarchical control which directly accounts for interactions among these systems and timescales. However, time-based hierarchical control is highly susceptible to unknown, unanticipated disturbances and faults due to the slow update rates of upper-level controllers. Vehicle systems in particular need the ability to quickly respond and reject the effects of these faults and disturbances. Therefore, an event-based triggering approach is presented, allowing controllers to update in response to a fault instead of waiting for the next time-based update. Results based on a simulated aircraft system show that event-based hierarchical control can significantly reduce the effect of these faults.